Knowing whether to use “whether” or “if”

When introducing a clause indicating uncertainty after a verb, is it better to use “whether” or ‘if”?

That’s a question the editors at Precision Science Editing are frequently asked. Although the two words are often used interchangeably in informal writing, as theAmerican Heritage Guide to Contemporary Usage and Stylepoints out, ”Whether has long been the preferred word in more formal contexts.”

“Use ‘if’ when you have a conditional sentence and ‘whether’ when showing that two alternatives are possible.”

Compare these two statements:

The laboratory assistant didn’t know if the specimens would arrive on Friday or Saturday.(This statement implies the specimens may arrive on Friday, on Saturday, or not at all!)

The laboratory assistant didn’t know whether the specimens would arrive on Friday or Saturday.(This statement implies there were only two possibilities: the specimens would arrive on Friday or they would arrive on Saturday.

The GMAT Tip of the Week, a weekly column that includes advice on taking the Graduate Management Admission Test, explains it this way:

Use “if” in a conditional sentence to show that one thing will happen if something else happens. Use “whether” to show that two alternatives are possible.

If it rains, they will collect stormwater samples.

They will do their field sampling regardless of whether it rains.

The word “whether” can be used:

After a preposition:

Have you settled the question of whether there is a direct causative relation between Chlamydia trachomatis and PID?

Before an infinitive:

This stage of our work is focused on helping us decide whether to continue testing for the presence of Streptococcus pneumoniae in all patients admitted to northern Indiana hospitals over the coming month.

As a subject:

Whether the project will receive funding is yet to be determined.

In a two-part phrase or question (i.e., when two alternatives are posed):

Whether or not there is definitive evidence of the presence of endospore-forming bacteria, implementation of prophylactic measures is recommended.

The word “whether” can be used as the complement in a sentence:

Given the lack of data on the direct effect night work has on the suppression of melatonin production, the question is whether there is enough interest in the research effort and, therefore, whether adequate research funding can be obtained.

Not sure whether to use “whether”? “If” should be used when you have a conditional sentence. When only two alternatives are possible, “whether” is the better choice.

Rick of the Precision Science Editing blog teamKnowing whether to use “whether” or “if”10.08.2015